Devices and methods for monoaxial screw conversion

ABSTRACT

Devices and methods for selectively converting polyaxial bone screws into monoaxial screws are described herein. In one embodiment, a spinal screw extension instrument is provided having an outer component configured to engage a receiving member of a polyaxial screw. The instrument further includes an inner component disposed within an inner lumen of the outer component and configured to translate longitudinally relative to the outer component such that the inner component can apply a distal force to a compression member of the polyaxial screw disposed within a distal portion of the receiving member to thereby convert the polyaxial screw to a monoaxial screw.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/831,430, filed on Mar. 14, 2013, now issued as U.S. Pat. No.9,216,043 and entitled “DEVICES AND METHODS FOR MONOAXIAL SCREWCONVERSION.” The teachings of the aforementioned application areincorporated herein by reference in their entirety.

FIELD

The present invention relates to methods and devices for use in spinalsurgery and, in particular, to instruments and methods for use duringspinal fixation procedures.

BACKGROUND

Spinal fixation devices are used in orthopedic surgery to align and/orfix a desired relationship between adjacent vertebral bodies. Suchdevices typically include a spinal fixation element, such as arelatively rigid fixation rod, that is coupled to adjacent vertebrae byattaching the element to various anchoring devices, such as hooks,bolts, wires, or screws. Alternatively, two rods can be disposed on thelateral or anterior surface of the vertebral body in a substantiallyparallel relationship. The fixation rods can have a predeterminedcontour that has been designed according to the properties of the targetimplantation site and, once installed, the rods hold the vertebrae in adesired spatial relationship, either until desired healing or spinalfusion has taken place, or for some longer period of time.

Spinal fixation devices can be anchored to specific portions of thevertebra. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a receiving member having a U-shaped slot forseating the fixation rod. The receiving member can be monoaxial and thusfixed relative to the threaded shank, or it can be polyaxial and thusmovable relative to the threaded shank. Polyaxial screws can facilitatepositioning of the fixation rod therein. Extension instruments are oftencoupled to the receiving member, especially in minimally invasiveprocedures, to provide a pathway through tissue to the receiving member.A set screw, plug, or similar type of closure mechanism, is used to lockthe fixation rod into the receiving member of the pedicle screw.

While current spinal fixation systems have proven effective,difficulties have been encountered in mounting rods into the receivingmember of various fixation devices. In particular, it can be difficultto align and seat the rod into the receiving portion of adjacentfixation devices due to the positioning and rigidity of the vertebrainto which the fixation device is mounted. While polyaxial pediclescrews can facilitate positioning of the fixation rod within thereceiving member, additional correction of spinal deformities is oftenrequired. For example, the alignment of multiple vertebral levels canrequire manipulation of the extension instruments at each level toachieve the desired results. During these manipulation steps, thepolyaxial screw is converted into a monoaxial screw to allow the surgeonto grasp the extension instrument and thereby manipulate the vertebracoupled thereto. While closure mechanisms can provide the ability tointraoperatively lock the polyaxial feature of the screw independent oflocking the fixation rod within the receiving member, the closuremechanism can only be utilized after the rod is positioned within thereceiving member, as it is inserted in a top-down fashion to press therod into the U-shaped slot. In an open procedure, the rod can often beplaced within the receiving member prior to correction, and thusconversion of the polyaxial screw into a monoaxial screw can often beachieved using the closure mechanism. In a minimally invasive deformitycorrection procedure, however, surgeons often utilize a “rod second”approach. This means that the spine is provisionally corrected prior toplacing the rod within the receiving member. In a “rod second” approachthe closure mechanism cannot be utilized to convert the polyaxial screwinto a monoaxial screw.

Accordingly, there is a need for devices and methods forintraoperatively and selectively converting a polyaxial screw into amonoaxial screw to facilitate deformity correction and other operationsduring spinal surgery.

SUMMARY

The present invention generally provides devices and methods forintraoperatively and selectively converting a polyaxial screw into amonoaxial screw. Such devices and methods can be used, for example,during spinal surgery to aid surgeons in correcting deformities orotherwise manipulating a patient's vertebrae during an operation. Thedevices and methods described herein are designed for use with a varietyof known polyaxial screw configurations. In some embodiments, thedevices can include an outer component configured to couple with areceiving member of a polyaxial screw and an inner component configuredto translate longitudinally with respect to the outer component. Bytranslating the inner component distally while the outer component iscoupled to a polyaxial screw, the distal end of the inner component canapply a distal force to a portion of the polyaxial screw and preventpolyaxial movement between the receiving member and a threaded shank ofthe bone screw. In such a configuration, the polyaxial screw iseffectively converted into a monoaxial screw. The devices and methodsdescribed herein are particularly advantageous because the conversionbetween a polyaxial and a monoaxial screw is selective and reversible.This allows surgeons the freedom to either move or restrain thereceiving member when desired, thereby permitting a single polyaxialscrew to be used for a variety of procedures.

In one aspect, a spinal screw extension instrument is provided thatincludes an outer component having an inner lumen extending therethroughand a distal end with opposed arms configured to engage a receivingmember of a polyaxial screw such that opposed slots formed between theopposed arms are aligned with opposed slots formed in the receivingmember. The instrument further includes an inner component disposedwithin the inner lumen of the outer component and having a distal endwith opposed arms and opposed slots formed between the opposed arms. Theinner component can be configured to translate longitudinally relativeto the outer component such that the opposed slots of the innercomponent are aligned with the opposed slots of the outer component andthe receiving member. Further, the opposed arms of the inner componentcan be configured to apply a distal force to a compression member of thepolyaxial screw disposed within a distal portion of the receiving memberto thereby convert the polyaxial screw to a monoaxial screw.

The devices and methods described herein can include a number ofadditional features or variations, all of which are considered withinthe scope of the invention. For example, in some embodiments, the distalend of the inner component can extend distally beyond the distal end ofthe outer component when applying the distal force to the compressionmember of the polyaxial screw. Further, in some embodiments, the innercomponent can include a surface feature to prevent rotation relative tothe outer component during longitudinal translation. Exemplary surfacefeatures can include a pin, setscrew, or other protrusion that extendsfrom a surface of one component (e.g., from the outer surface of theinner component or the inner surface of the outer component) andinterfaces with a slot or other recess formed on the other component.

In certain embodiments, a proximal portion of the inner component can beconfigured to threadably engage with the outer component such thatrotation of the proximal portion of the inner component can translatethe inner component relative to the outer component. In such anembodiment, the proximal portion of the inner component can be rotatablycoupled to a distal portion of the inner component such that the distalportion of the inner component can be restrained from rotating with theproximal portion (e.g., using the surface feature and complementaryrecess described above). In some embodiments, the rotatable coupling canbe accomplished by providing a circumferential groove or recess formedin one portion (e.g., the proximal or distal portion of the innercomponent) and a pin formed in the other portion that seats within thegroove to hold the two portions together but allow relative rotationtherebetween. As a result, the distal portion of the inner component cantranslate without rotating relative to the outer component when theproximal portion is rotated to effect the translation of the innercomponent.

In other embodiments, the instrument can include an actuator coupled tothe outer component and the inner component. The actuator can beconfigured to effect the longitudinal translation of the inner componentrelative to the outer component. In some embodiments, the actuator caninclude a threaded outer surface configured to engage with a threadedsurface of the inner lumen of the outer component. In other embodiments,however, the actuator can include an inner lumen having a threadedsurface configured to engage with a threaded outer surface of the innercomponent. In still other embodiments, the actuator can include both athreaded outer surface and an inner lumen having a threaded surface, andthe threads on the surface of the inner lumen can be opposite-handed ofthe threaded outer surface.

The outer and inner components can have a variety of shapes andmechanical configurations. In some embodiments, the outer component caninclude opposed portions coupled such that the opposed arms at thedistal end of the outer component are biased toward one another. Incertain embodiments, the instrument can also include a retaining ringcoupled to one of the opposed portions and encircling both opposedportions. The retaining ring can provide support against torsionaldeformation and limit how close the opposed arms at the distal end ofthe outer component are allowed to come.

In still other embodiments, the outer component can include an outersleeve configured to engage a feature formed on an outer surface of thereceiving member of the polyaxial screw, as well as an inner sleevedisposed within the outer sleeve and configured to abut against an uppersurface of the receiving member of the polyaxial screw. The two sleeves,working in tandem, can securely engage the receiving member of thepolyaxial screw.

In another aspect, a spinal fixation kit is provided that includes apolyaxial screw and a screw extension instrument. The polyaxial screwcan include a threaded shank having a head formed on a proximal endthereof and a receiving member having a spherical seat formed in adistal portion thereof for seating the head formed on the threadedshank. The receiving member can also include an aperture extendingthrough a distal end thereof to allow the threaded shank to extenddistally from the receiving member. The polyaxial screw can furtherinclude a compression member disposed within the receiving member andhaving a first position in which the receiving member is polyaxiallymovable relative to the threaded shank, and a second position in whichthe compression member engages the head formed on the threaded shank tolock the threaded shank in a fixed position relative to the receivingmember and thereby convert the polyaxial screw into a monoaxial screw.The screw extension instrument can include an outer component with adistal end configured to engage the receiving member such that opposedslots formed in the distal end of the outer component align with opposedslots formed in the receiving member. The screw extension instrument canfurther include an inner component coupled to the outer component andconfigured to longitudinally translate relative to the outer component.The inner component can have a distal end with opposed slots that arealigned with the opposed slots of the outer component and the receivingmember, and the inner component can be configured to advance distally toapply a distal force to the compression member to move the compressionmember from the first position to the second position. This movement caneffectively convert the polyaxial screw into a monoaxial screw untilsuch time as the distal force from the inner component is removed.

As with the device described above, several variations and additionalfeatures can be included in the kit. For example, in some embodimentsthe inner component can extend distally beyond the distal end of theouter component when the compression member of the polyaxial bone screwis in the second position.

As described above, in some embodiments a proximal portion of the innercomponent can be configured to threadably engage with the outercomponent such that rotation of the proximal portion of the innercomponent can translate the inner component relative to the outercomponent. In such an embodiment, the proximal portion of the innercomponent can be rotatably coupled to a distal portion of the innercomponent such that the distal portion of the inner component can berestrained from rotating with the proximal portion (e.g., using thesurface feature and complementary recess described above). As a result,the distal portion of the inner component can translate without rotatingrelative to the outer component when the proximal portion is rotated.

In other embodiments, the screw extension instrument can include anactuator coupled to the outer component and the inner component. Theactuator can be configured to effect the longitudinal translation of theinner component relative to the outer component. The actuator can, insome embodiments, include a threaded outer surface configured to engagewith a threaded surface of the outer component. In other embodiments,the actuator can include a threaded inner lumen configured to engagewith a threaded outer surface of the inner component. Still further, incertain embodiments the actuator can include both a threaded outersurface and an inner lumen with a threaded surface, and the threads ofthe inner lumen can be opposite-handed of the threaded outer surface.

The outer and inner components can have a variety of shapes andmechanical configurations. In some embodiments, for example, the outercomponent can include opposed portions coupled such that the distal endsof the opposed portions of the outer component are biased toward oneanother. In still other embodiments, the screw extension instrument caninclude a retaining ring coupled to one of the opposed portions of theouter component and encircling both of the opposed portions. Theretaining ring can provide support against torsional deformation andlimit how close the distal ends of the opposed portions of the outercomponent are allowed to come.

In another aspect, a method for correcting spinal deformities isprovided that includes coupling a screw extension instrument to areceiving member of a polyaxial screw, where the receiving member iscoupled to a threaded shank that is polyaxially movable relative to thereceiving member. The method can further include advancing an innercomponent of the screw extension instrument relative to the receivingmember of the polyaxial screw to cause the inner component to convertthe polyaxial screw into a monoaxial screw.

In certain embodiments, advancing the inner component of the screwextension instrument can include pushing a compression member disposedwithin a distal portion of the receiving member of the polyaxial screwonto a head formed on the threaded shank of the polyaxial screw tothereby prevent movement of the head relative to the receiving member.Once movement of the head relative to the receiving member isrestricted, the polyaxial bone screw is effectively converted into amonoaxial bone screw.

In some embodiments, the method can further include implanting thethreaded shank of the polyaxial screw in a vertebra before coupling thescrew extension instrument to the receiving member of the polyaxialscrew. However, in other embodiments, the order can be reversed and themethod can include implanting the threaded shank of the polyaxial screwin a vertebra after coupling the screw extension instrument to thereceiving member of the polyaxial screw.

In certain embodiments, the method can further include passing a spinalfixation rod through the receiving member of the polyaxial screw afteradvancing the inner component of the screw extension instrument toconvert the polyaxial screw into a monoaxial screw. For example, incertain “rod second” approaches to spinal deformity correction, asurgeon will provisionally correct the position of a vertebra beforeinserting a rod. In order to be able to manipulate the vertebra, thesurgeon can convert the polyaxial screw into a monoaxial screw, performthe provisional correction, and then pass the spinal fixation rodthrough the receiving member.

In some embodiments, it can be desirable to convert the monoaxial screwback into a polyaxial screw after, for example, provisionally correctingthe position of a vertebra. This is because the polyaxial movement ofthe receiving head can make it easier to capture the spinal fixationrod. As a result, the method can, in some embodiments, includeretracting the inner component of the screw extension instrumentrelative to the receiving member to convert the monoaxial screw into apolyaxial screw after advancing the inner component of the screwextension instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments of the invention described above will bemore fully understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a prior art polyaxial screw;

FIG. 2 is a front cross-sectional view of the prior art polyaxial screwof FIG. 1;

FIG. 3 is a perspective view of an alternative embodiment of a prior artreceiving member of a polyaxial screw;

FIG. 4 is a perspective view of another alternative embodiment of aprior art receiving member of a polyaxial screw;

FIG. 5 is a perspective cross-sectional view of one embodiment of ascrew extension instrument;

FIG. 6 is a perspective view of an outer component of the screwextension instrument of FIG. 5;

FIG. 7 is a perspective view of an inner component of the screwextension instrument of FIG. 5;

FIG. 8 is a perspective view of an actuator of the screw extensioninstrument of FIG. 5;

FIG. 9 is an exploded view of one embodiment of an inner component;

FIG. 10A is a perspective view of an alternative embodiment of a screwextension instrument;

FIG. 10B is a perspective view of a distal end of the device shown inFIG. 10A;

FIG. 11 is a front cross-sectional view of the distal end of the deviceshown in FIG. 9;

FIG. 12A is a perspective view of an implanted polyaxial screw attachedto a screw extension instrument;

FIG. 12B is a close perspective view of the polyaxial screw of FIG. 10Ashowing the outer component coupled to the polyaxial screw;

FIG. 12C is a close perspective view of the polyaxial screw of FIG. 10Ashowing the inner component translated distally to convert the polyaxialscrew into a monoaxial screw;

FIG. 13A is a perspective view of an alternative embodiment of an outercomponent of a screw extension instrument;

FIG. 13B is a perspective view of an alternative embodiment of apolyaxial screw configured for use with the screw extension instrumentof FIG. 13A;

FIG. 14A is a perspective view of an alternative embodiment of an outercomponent of a screw extension instrument;

FIG. 14B is a perspective view of an alternative embodiment of areceiving member of a polyaxial screw configured for use with the screwextension instrument of FIG. 14A; and

FIG. 14C is an alternative perspective view of the receiving member ofFIG. 14B.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the devices and methodsdisclosed herein. One or more examples of these embodiments areillustrated in the accompanying drawings. Those skilled in the art willunderstand that the devices and methods specifically described hereinand illustrated in the accompanying drawings are non-limiting exemplaryembodiments and that the scope of the present invention is definedsolely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.

The present invention is generally directed to devices and methods forintraoperatively and selectively converting a polyaxial bone screw intoa monoaxial bone screw. Such devices and methods can be used, forexample, during spinal surgery to aid surgeons in correcting deformitiesor otherwise manipulating a patient's vertebrae during an operation. Thedevices and methods described herein are designed for use with a varietyof known polyaxial screw configurations. The devices described hereingenerally include an outer component configured to couple with areceiving member of a polyaxial screw and an inner component configuredto translate longitudinally with respect to the outer component andreceiving member. By translating the inner component distally while theouter component is coupled to a polyaxial screw, the distal end of theinner component can apply a distal force to a portion of the polyaxialscrew and prevent polyaxial movement between a receiving member and athreaded shank of the screw. In such a configuration, the polyaxialscrew is effectively converted into a monoaxial screw. The devices andmethods described herein can be particularly advantageous because theconversion between a polyaxial and a monoaxial screw is selective andreversible. This allows surgeons the freedom to either move or restrainthe receiving member when desired, thereby permitting a single polyaxialscrew to be used for a variety of procedures. Furthermore, the devicesdescribed herein are able to provide this selective conversion betweenpolyaxial and monoaxial configurations without preventing the passage ofa spinal fixation element through the receiving member of the screw.

FIG. 1 illustrates one embodiment of a polyaxial screw 100 known in theart. The polyaxial screw 100 includes a bone anchor 102, such as apedicle screw, having a proximal head 104 and a distal bone-engagingportion 106, which in the illustrated exemplary embodiment is anexternally threaded screw shank. The polyaxial screw 100 also includes areceiving member 108 that is configured to receive and couple a spinalfixation element, such as a spinal rod or spinal plate, to the polyaxialscrew 100.

The receiving member 108 may be coupled to the bone anchor 102 in anymanner known in the art. For example, the bone anchor 102 may beadjustable to multiple angles relative to the receiving member 108. Thisis in contrast to monoaxial bone screws, in which the bone anchor 102and the receiving member 108 are not movable relative to one another. Anexemplary polyaxial bone screw is described U.S. Pat. No. 5,672,176,which is herein incorporated by reference in its entirety.

The receiving member 108 of the illustrated exemplary embodimentincludes a proximal end 110, a distal end 112, and a recess or slot 114for receiving a spinal fixation element, such as a spinal rod. Theproximal end 110 of the receiving member 108 has a first bore 116 formedtherein that defines a first bore axis 118 and communicates with therecess 114 such that a spinal fixation element may be positioned throughthe first bore into the recess 114. The distal end 112 has a second bore120 opposite the first bore 116 that defines a second bore axis 122 andis designed to receive the head 104 of the bone anchor 102 to couple thebone anchor to the receiving member 108. In the illustrated exemplaryembodiment, the head 104 is seated within the second bore 120. As theexemplary illustrated embodiment of the bone anchor assembly ispolyaxial, the bone anchor 102 is free to rotate relative to thereceiving member 108 such that the longitudinal axis 124 of the boneanchor 102 is positionable at an angle relative to the second bore axis122 of the receiving member 108 (in FIG. 1, the first bore axis 118,second bore axis 122, and longitudinal axis 124 of the bone anchor 102are coaxial). The second bore 120 may be spherically or conically shapedto facilitate adjustment of the bone anchor 102 relative to thereceiving member 108. In the exemplary embodiment, the receiving member108 has a generally U-shaped cross-section defined by two legs 124A and124B separated by recess 114. Each leg 124A, 124B is free at theproximal end 110 of the receiving member 108.

The receiving member 108 may be configured to receive a closuremechanism that locks a spinal fixation element within the recess 114.The closure mechanism may be a cap that is advanceable through the firstbore 116 of the receiving member 108 and seats against the spinalfixation element. For example, the cap may have external threads thatengage internal threads provided in the receiving member 108, e.g., onthe legs 124A, 124B. Any type of conventional closure mechanism may beemployed, including, for example, non-threaded caps, multi-componentclosure mechanisms, and/or external caps.

The receiving member 108 of the exemplary polyaxial screw 100 caninclude features allowing it to be releasably connected to aninstrument, such as the screw extension instrument described below. Forexample, the receiving member 108 may include at least one groove 130that is configured to receive a portion of an instrument to releasablyconnect the instrument to the polyaxial screw. The size, shape,position, and number of grooves can be varied depending on, for example,the instrument employed and the type of connection desired. In certainembodiments, for example, at least one arcuate groove 130 may beprovided on an exterior surface of the proximal end 110 of the receivingmember 108. In other exemplary embodiments, at least one arcuate groovemay be provided on an interior surface of the proximal end 110 of thereceiving member 108. In the illustrated exemplary embodiment, each leg124A and 124B may be provided with an arcuate groove 130A, 130B,respectively, at the free, proximal end of the leg 124A, 124B. Thegrooves 130A, 130B may extend about a portion or the entirety of thecircumference of the proximal end of each leg 124A, 124B. Each groove130A, 130B may have a size and shape that is complementary in size andshape to a projection or other feature provided on the instrument, asdescribed in more detail below.

FIG. 2 illustrates the polyaxial screw 100 in cross-section. Inparticular, the spherical head 104 of the bone anchor 102 is shownextending through the second bore 120 formed in the distal end of thereceiving member 108 and seated within a spherical seat in the receivingmember. The head 104 can include a recess 202 or other feature that canreceive a driver or other instrument that can be used to implant thebone anchor 102 in a vertebra. Also shown is a compression member 204that resides within the recess 114 of the receiving member 108. Thecompression member 204 can include an inner lumen that allows a driveror other instrument to access the recess 202 of the bone anchor 102.Furthermore, the compression member 204 can include features formed atits proximal and distal ends that are configured to interface with aspinal fixation element, such as the spinal fixation rod 206, and thehead 104 of the bone anchor 102, respectively. For example, thecompression member 204 can include a hemispherical recess 208 formed atits distal end that can mirror the shape of the head 104 of the boneanchor 102. At its proximal end, the compression member 204 can includea U-shaped recess 210 that is configured to seat a spinal fixationelement, such as the spinal fixation rod 206.

The compression member 204 can be configured to travel within the recess114 of the receiving member 108 along the first bore axis 118 between afirst position in which the compression member allows polyaxial movementof the head 104 within the receiving member 108 and a second position(shown by arrows 212 in FIG. 2) in which the compression member locksthe orientation of the bone anchor 102 with respect to the receivingmember 108. This is typically accomplished with the use of a closuremechanism, such as the outer set screw 214. As the outer set screw 214is threaded into the proximal end of the receiving member 108, it canexert a downward force on the compression member 204 (shown by arrows216 in FIG. 2), thereby pushing the compression member 204 from thefirst position to the second position and locking the orientation of thebone anchor 102 and the receiving member. The outer set screw 214 canitself include an inner lumen to receive an inner set screw 218 that canbe used to lock the receiving member in a particular orientation andposition along the spinal fixation rod 206 by pressing the rod into theU-shaped recess 210 of the compression member (shown by arrows 216 inFIG. 2).

There are a number of variations on the polyaxial screw 100 known in theart. For example, FIG. 3 illustrates an embodiment of a polyaxial screwreceiving member 300 that is biased to a particular angle or range ofangles to provide a favored angle to the bone anchor 102. This favoredangle can aid in rod capture during a spinal procedure as the receivingmember 108 can have additional range of motion in one direction, e.g.,laterally away from the spinal column. In favored angle embodiments, thesecond bore axis 122 can be positioned at an angle α (other than 0°) tothe first bore axis 118. Exemplary favored angle bone screws aredescribed in U.S. Pat. Nos. 6,736,820 and 6,974,460, both of which areherein incorporated by reference in their entirety.

In other embodiments, polyaxial screws can include features to extendthe legs 124A, 124B, as shown in FIG. 4. In the illustrated embodiment,the opposed legs 402A, 402B of the receiving member 400 each includetabs 404A, 404B extending from a proximal end of the receiving member400. The tabs 404A, 404B can have a generally arcuate shape and can beconfigured to allow an instrument to releasably engage with thereceiving member 400. The tabs 404A, 404B can include a feature orfeatures for facilitating releasable engagement by an instrument. Forexample, the tabs can be provided with external threads, or can includeone or more grooves. In the illustrated exemplary embodiment, each tab402A, 402B includes one or more arcuate grooves 404A, 404B that may beanalogous in construction to the grooves 130A, 130B described above. Thetabs 402A, 402B can also include internal threads 406 to facilitateadvancement of a closure mechanism, such as the outer set screw 214discussed above, to the receiving member 400. Tabs 404A, 404B can besheared off the receiving member 400 after a closure mechanism isapplied to secure the position of the receiving member 400 and/or aspinal fixation element extending therethrough.

Surgical procedures to correct deformities or other abnormalities of thespine using the polyaxial screws described above typically involveimplanting one or more polyaxial screws in the vertebrae that are to beadjusted, and using a spinal fixation element spanning across thepolyaxial screws to impart and maintain a desired shape in the spine.Methods for performing these procedures typically involve implanting aplurality of polyaxial screws, capturing a spinal fixation elementwithin the receiving members of the polyaxial screws, and then applyinga closure mechanism, such as the outer and inner set screws describedabove, to lock the fixation element within the receiving members of thepolyaxial screws. The polyaxial screws described above can beparticularly advantageous because the independent functionality of theouter and inner set screws can allow the polyaxial screw to beintraoperatively converted into a monoaxial screw. Converting apolyaxial screw to a monoaxial screw intraoperatively can allow for moreeffective adjustment of the position and/or orientation of a givenvertebra as forces are applied to the screw.

In certain procedures, however, surgeons adopt a “rod second” approach,in which the spine is provisionally corrected prior capturing a rod orother spinal fixation element within the receiving members of theimplanted bone screws. This is especially popular in minimally invasivesurgical (MIS) procedures, where the patient's spine is not whollyexposed during the operation and provisional correction of the spine'sshape can facilitate easier percutaneous introduction of a spinalfixation rod or other element. To date, it has been impossible toleverage the advantages of the polyaxial screws described above becausethe requirement of a set screw to facilitate the conversion makes itimpossible to pass a rod into the receiving member.

The present invention provides devices and methods that allow for theintraoperative and selective conversion of a polyaxial screw into amonoaxial screw while maintaining the ability to introduce a spinalfixation element into a receiving member of the screw. The devices andmethods described herein can allow a surgeon or other user to convert ascrew between polyaxial and monoaxial configurations as desiredthroughout a procedure (e.g., a polyaxial configuration can be preferredduring rod capture and a monoaxial configuration can be preferred duringderotation, fracture closure, and parallel compression or distractionprocedures). This provides a surgeon or other user with increasedflexibility to address anticipated or unforeseen difficulties that oftenoccur during technically challenging spinal operations.

FIG. 5 illustrates one embodiment of a screw extension instrument 500according to the teachings of the present invention. The screw extensioninstrument 500 is shown attached to the polyaxial screw 100 and having aspinal fixation rod 206 seated therein. As described above, thepolyaxial screw 100 includes a bone anchor 102 coupled to a receivingmember 108. The receiving member 108 includes a compression member 204disposed within a distal portion of the receiving member and configuredto move between a first position in which the bone anchor 102 can movepolyaxially with respect to the receiving member, and a second positionin which the bone anchor and the receiving member have a fixedorientation.

The screw extension instrument 500 can include an outer component 502,an inner component 504, and an actuator 506 coupled to the outercomponent and the inner component. The outer component 502 can haveopposed arms configured to releasably engage with the receiving member108 of the polyaxial screw 100 using, for example, features similar tothe groove 130 described above. The inner component 504, which isdisposed within an inner lumen of the outer component 502, can beconfigured to translate along the first bore axis 118 toward thecompression member 204 disposed in the distal end of the receivingmember 108. The inner component 504 can include opposed arms at a distalend thereof that are configured to apply a distal force to thecompression member 204, thereby converting the polyaxial screw 100 intoa monoaxial screw, as described above. The translation of the innercomponent 504 relative to the outer component 502 and the receivingmember 108 can be effected by the actuator 506, at least a part of whichcan be positioned at a proximal end of the instrument 500 for ease ofaccess. In addition, the alignment of the slots formed between theopposed arms of the outer component and the inner component with theU-shaped cross-section of the receiving member 108 allows for theintroduction of the spinal fixation rod 206 even when the polyaxialscrew is locked in a monoaxial configuration by the instrument 500.

FIG. 6 illustrates one embodiment of the outer component 502 of theinstrument 500. The outer component 502 can have a variety of shapes andsizes. In the illustrated embodiment, the outer component 502 has agenerally cylindrical shape and is formed from two opposed portions602A, 602B that define an inner lumen 603 extending therebetween. Theopposed portions can include opposed arms 608A, 608B formed at a distalend of the outer component, and opposed tabs 607A, 607B formed at aproximal end of the outer component. The opposed portions can be coupledtogether by connecting portions 604A, 604B that define a pivoting axis606 around which the opposed portions rotate toward or away from oneanother. Further, the connecting portions 604A, 604B can be formed suchthat the opposed portions 602A, 602B of the outer component 502 arebiased toward or away from each other at the proximal and distal ends ofthe outer component. For example, in the illustrated embodiment, opposedarms 608A, 608B formed at the distal end of the opposed portions 602A,602B can be biased toward one another and, correspondingly, the tabs607A, 607B formed at the proximal ends of the opposed portions 602A,602B can be biased away from one another. As a result, the outercomponent 502 can function similarly to a clothespin when releasablyengaging with the receiving member 108 of the polyaxial screw 100.

The opposed arms 608A, 608B at the distal end of the outer component 502can have a variety of shapes and sizes as well. In some embodiments, theopposed arms 608A, 608B can have a generally arcuate shape incross-section and can define opposed slots 609A, 609B extending betweenthe arms. The opposed arms can, in some embodiments, include featuresdesigned to facilitate engagement with the receiving member 108. Forexample, the inner surface of each arm can include a protrusion orrecess configured to interface with a complementary feature formed on anouter surface of the receiving member 108. For example, in theillustrated embodiment, the inner surface of the opposed arms 608A, 608Bcan include a protrusion 610 configured to interface with the groove 130of the receiving member 108. In addition, the outside edges of theopposed arms 608A, 608B can include contact surfaces 612 configured toabut against contact surfaces 152 (see FIG. 1) of the receiving memberlegs 124A, 124B. The contact surfaces 612 are similar to the finger-likeextensions 82 described below (see FIG. 10) and can prevent the rotationof the receiving member 108 with respect to the outer component 502.

To releasably engage the outer component with the receiving member 108of the polyaxial screw 100, a user can pinch the tabs 607A, 607B at theproximal end of the outer component 502 together using their hand or atool. This action pivots the opposed portions 602A, 602B around thepivoting axis 606 and separates the opposed arms 608A, 608B at thedistal end of the outer component. The receiving member 108 can then beadvanced into the inner lumen 603 of the outer component between theopposed arms 608A, 608B. The tabs 607A, 607B can be released and thebias imparted by the connecting portions 604A, 604B can clamp theopposed arms 608A, 608B onto the receiving member 108 such that thereceiving member and the outer component are securely coupled together.

The outer component 502 can also include a retaining ring 508 (alsovisible in cross section in FIG. 5) coupled thereto at a locationproximal to the pivoting axis 606. The retaining ring can be sized suchthat it encircles the opposed portions 602A, 602B without excessclearance at a desired maximum separation between the opposed portions.The retaining ring 508 can provide resistance to shear forces actingalong the pivoting axis 606. The retaining ring 508 can be coupled toone of the opposed portions 602A, 602B and can remain unattached to theother such that the retaining ring does not interfere with the abilityof the opposed portions to pivot relative to one another to bring theopposed tabs 607A, 607B closer together. This can be accomplished, forexample, by welding, mechanically fastening, or chemically adhering theretaining ring to one of opposed portion 602A or 602B.

Still further, the outer component 502 can include features tofacilitate the longitudinal translation of the inner component withrespect thereto. For example, an inner surface of the outer component(i.e., a surface of the inner lumen 603) can include threads 512 (alsovisible in cross-section in FIG. 5) to accept the actuator 506 thateffects the translation of the inner component with respect to the outercomponent. Furthermore, opposing slots 622 (only one is visible in FIG.6) can extend from the connecting portions 604A, 604B to the proximalend of the outer component and can be configured to accept a protrusion710 (see FIG. 7) formed on an outer surface of the inner component 504to prevent the inner component from rotating during translation.

FIG. 7 illustrates one embodiment of the inner component 504 of thescrew extension instrument 500. The inner component can have a varietyof shapes and sizes but, in some embodiments, is a generally cylindricalbody having opposed arms 702A, 702B formed at a distal end thereof withopposed slots 704A, 704B formed between the opposed arms. The arms canhave a variety of shapes and sizes themselves, but in some embodimentsare sized such that they can extend into the recess 114 of the receivingmember 108 without interfering with the passage of a spinal fixationelement, such as rod 206. In addition, the distal faces of the opposedarms 702A, 702B can have a shape, such as a planar surface, configuredto interface with an upper surface of the compression member 204,thereby allowing the opposed arms to effectively impart a distal forceonto the compression member.

The proximal end of the inner component can include a threaded outersurface 706 configured to threadably mate with the actuator 506. Thethreads formed on the outer surface of the inner component 504 can beopposite-handed from the threads formed on the inner lumen 603 of theouter component 502 (e.g., the threads formed on the outer component 502can be right-handed and the threads formed on the inner component 504can be left-handed). In such a configuration, a single turn of theactuator 506 can translate the inner component 504 with respect to theouter component by twice the pitch of the threads. In addition, thethreads formed on the various surfaces of the screw extension instrument500 can be square or buttress threads (i.e., having a square orpartially-square cross-sectional profile), as these profiles canmaximize the transmission of force between the components along thelongitudinal axis of the instrument 500.

In addition, the proximal end of the inner component can include a stop708 to prevent the inner component from retracting too far into theactuator 506 as it is rotated. Still further, the inner component caninclude one or more protrusions 710 or other features formed on an outersurface thereof. The one or more protrusions 710 can be configured tointerface with one or more features of the outer component 502, such asthe opposed slots 622, to prevent the inner component from rotating withrespect to the outer component as it translates longitudinally. In otherembodiments, however, the orientation of these features can be reversed.For example, a protrusion, pin, set screw, or other feature can beformed on an inner surface of the outer component 502 and a slot orother complementary recess can be formed on an outer surface of theinner component 504. Regardless of the orientation, the interaction of aprotruding feature and a complementary slot or recess can preventundesired rotation of the inner component relative to the outercomponent.

The inner component 504 can have a constant outer diameter, as shown inFIG. 7, or it can include portions having different diameters, as shownin FIG. 5. For example, in an embodiment in which the outer diameter ofa proximal portion of the inner component 504 is larger than a diameterof the first bore 116, a distal portion 514 of the inner component 504can have a reduced diameter such that the inner component can fit withinthe recess 114 of the receiving member 108. The reduced diameter portion514 can extend for any desired length toward the proximal end of theinner component 104 (up to and including the entire length of the innercomponent, as shown in FIG. 7). In embodiments in which receivingmembers with extending tabs (e.g., tabs 404A, 404B shown in FIG. 4) areutilized, the reduced diameter portion 514 can extend for at least thelength of the extending tabs (thus, the extending tabs would beaccommodated in the space visible between the reduced diameter portion514 and the outer component 502 in FIG. 5).

Moreover, in some embodiments, the inner component 504 can also includean inner lumen 516 extending therethrough. The inner lumen 516 can allowadditional instruments to be inserted therethrough to access thepolyaxial screw 100. Exemplary instruments can include a rod pusher thatcan be used to press a spinal fixation rod into the receiving member108, or a bone anchor driver that can be used to implant the bone anchor102 into a vertebra.

FIG. 8 illustrates one embodiment of the actuator 506 of the screwextension instrument 500. The actuator 506 can have a variety of shapesand sizes. In one embodiment, the actuator 506 has a generallycylindrical shape and is configured to be threadably mated with theouter component 502 from the proximal end of the outer component. Theactuator 506 therefore includes a threaded outer surface 802 at a distalend thereof. The actuator 506 can also include an inner lumen 518extending therethrough that can communicate with the inner lumen 516 ofthe inner component 504, thereby allowing other tools or instruments tobe passed through the screw extension instrument 500 down to thepolyaxial screw 100. A distal portion 520 of the inner lumen 518 of theactuator can include threads that are opposite-handed of the threadedouter surface 802. The threads can be configured to interface with thethreaded outer surface 706 of the inner component 504. A proximalportion 522 of the inner lumen 518 can have a cross-sectional profileconfigured to interface with a driver or other tool that can be used torotate the actuator. In addition, an outer surface of the actuator 506can include gripping features 804 along a proximal portion thereof toallow for hand manipulation if a driver or other tool is not used.

The actuator can also include a stopping pin or protrusion 510 mountedin a sidewall thereof and extending into the inner lumen 518. Thestopping pin 510 can be configured to abut against the stop 708 formedon the proximal end of the inner component 504, thereby preventing theinner component from being retracted too far into the inner lumen 518 ofthe actuator 506 during operation.

Furthermore, the actuator can include an enlarged diameter portion 524formed along a portion thereof proximal to the threaded outer surface802. The enlarged diameter portion 524 can extend toward the proximalend of the actuator by any length, and may extend to the proximal end ofthe actuator, resulting in an actuator having a single diameter proximalof the threaded outer surface 802. The enlarged diameter portion 524 canbe configured to abut against an inner surface of the tabs 607A, 607B ofthe outer component 502, preventing the tabs from being pinchedtogether. This can aid in securing the connection between the opposedarms 608A, 608B and the receiving member 108, as the tabs 607A, 607Bmust be pinched together in order to separate the opposed arms 608A,608B and release the receiving member 108. The actuator 506, incombination with the retaining ring 508, can provide a very secureconnection between the screw extension instrument and the polyaxialscrew. The rigidity and support provided by the screw extensioninstrument 500 can allow a surgeon or other user to directly manipulatethe outer component in order to adjust the position and/or orientationof the vertebra coupled to the screw. This can in some embodimentseliminate the need for additional facilitators or other instruments toaid in manipulation of the vertebra.

Referring back to FIG. 5, the operation of the screw extensioninstrument 500 can be explained in more detail. To begin, the outercomponent 502 can be separated from the inner component 504 and theactuator 506. This can be done, for example, by rotating the actuator506 in a counter-clockwise direction until the threaded outer surface802 of the actuator 506 disengages from the threads 512 formed on theinner surface of the outer component 502. Given the opposite-handedthreads formed on the outer and inner surfaces of the actuator 506, incombination with the protrusion 710 that prevents rotation of the innercomponent 504, the counter-clockwise rotation will cause the innercomponent 504 to retract into the inner lumen 518 of the actuator 506.Once the threaded outer surface 802 disengages from the outer component502, the inner component 504 and actuator 506 can be withdrawn from theproximal end of the outer component 502.

The opposed tabs 607A, 607B at the proximal end of the outer component502 can then be compressed together to draw the opposed arms 608A, 608Bapart at the distal end of the outer component. The receiving member 108of the polyaxial screw 100 can be placed between the opposed arms 608A,608B such that the opposed slots 609A, 609B align with the opposedU-shaped slots that extend between the opposed legs 124A, 124B of thereceiving member. The opposed tabs 607A, 607B can be released, allowingthe bias from the connecting portions 604A, 604B to draw the opposedarms 608A, 608B together and grasp the receiving member 108therebetween.

The inner component 504 and actuator 506 can then be inserted into theouter component 502 from a proximal end thereof. The protrusion 710 ofthe inner component can be aligned with the slot 622 of the outercomponent, which will also align the opposed slots 704A, 704B formedbetween the opposed arms 702A, 702B of the inner component 504 with theopposed slots 609A, 609B of the outer component 502 and those of thereceiving member 108. The actuator 506 can be rotated clockwise toengage the threaded outer surface 802 of the actuator 506 with thethreads 512 formed on the inner surface of the outer component 502. Theclockwise rotation that advances the actuator 506 distally relative tothe outer component also causes the inner component 504 to advancedistally out of the actuator due to the opposite-handed threads and theprotrusion 710 that prevents the inner component from rotating.Furthermore, as the actuator is advanced distally into the outercomponent 502, the enlarged diameter portion 524 of the actuator pressesagainst the inner surfaces of the opposed tabs 607A, 607B, urging thetabs away from one another and securing the coupling at the distal endbetween the receiving member 108 and the opposed arms 608A, 608B.

The actuator 506 can continue to be rotated clockwise to furtherdistally translate the inner component 504 relative to the outercomponent 502. The opposed arms 702A, 702B at the distal end of theinner component 504 can contact an upper surface of a compression memberdisposed in a distal portion of the receiving member 108 and apply adistal force thereto. The distal force can move the compression memberfrom a first position in which the threaded shank of the polyaxial screw100 is polyaxially movable relative to the receiving member to a secondposition in which the orientation of the threaded shank and thereceiving member are locked.

With the polyaxial screw converted to a monoaxial configuration, asurgeon or other user can directly manipulate the screw extensioninstrument 500 to adjust the position and/or orientation of the vertebrain which the polyaxial screw is implanted. Directly manipulating thescrew extension instrument can be advantageous because the largerinstrument provides an easier device to grip, and because in certainprocedures (e.g., MIS procedures), only the instrument may extend out ofthe patient's body above the patient's tissue and skin.

The polyaxial screw can be repeatedly converted between polyaxial andmonoaxial configurations by rotating the actuator until the desiredconfiguration is achieved, providing a surgeon or other user with agreat deal of flexibility in rod capture, derotation, fracture closure,and many other spinal surgery procedures. In addition, in someembodiments additional tools can be introduced down the inner lumens ofthe actuator and inner component to the polyaxial screw. Additionaldetails of an exemplary surgical procedure utilizing polyaxial screwsand spinal fixation elements are provided in U.S. Pat. No. 7,666,188,the contents of which are hereby incorporated by reference in theirentirety. When final positioning has been achieved, the inner componentand actuator can be removed from the outer component as described above,and a conventional closure mechanism can be inserted to permanently lockthe orientation of the polyaxial screw and secure the spinal fixationelement within the receiving member.

A number of variations of the embodiments shown in FIGS. 5-8 arepossible, all of which are considered within the scope of the invention.For example, there are several different variations on theabove-described embodiments that can be used to accomplish the desiredlongitudinal translation between the outer component 502 and the innercomponent 504. In one embodiment, the actuator can be eliminatedentirely, thereby allowing an inner component to threadably engagedirectly with the outer component. FIG. 9 illustrates an exemplaryembodiment of this type of inner component 920. The inner component 920includes a proximal portion 922 and a distal portion 924. The proximalportion 922 can include threads 926 formed on an outer surface thereofand configured to interface with threads formed on an inner surface ofan outer component, such as the threads 512. The proximal portion 922can also include a handle formed at a proximal end thereof (not shown)to allow an operator to rotate the proximal portion 922 by hand. Inanother embodiment, a proximal-most surface of the proximal portion 922can include a drive feature configured to mate with a drive tool thatcan be used to rotate the proximal portion 922.

The distal portion 924 can include opposed arms 928A, 928B that aresimilar to the opposed arms 702A, 702B discussed above. The proximal endof the distal portion 924, however, can be configured to rotatablycouple to the distal end of the proximal portion 922. In particular, theproximal portion 922 can include an inner lumen formed in a distal endthereof, and the inner lumen can be configured to receive a proximal end930 of the distal portion 922. The proximal end 930 of the distalportion 922 can further include a circumferential groove 932 formedtherein that can be seated within the inner lumen of the proximalportion 922 when the two portions are coupled together. One or more setscrews 934 can be inserted through a sidewall of the proximal portion922 as shown in the figure such that they sit within the groove 932 ofthe distal portion and prevent the two portions from decoupling. Inaddition, the set screws can allow the two portions to rotate relativeto one another. Moreover, the distal portion 924 can include one or moreprotrusions 936, similar to protrusions 710 discussed above, that caninterface with a slot (e.g., slot 622) or other feature formed in anouter component to prevent the distal portion 924 from rotating relativeto the outer component.

In another embodiment, the actuator 506 can be modified such that itdoes not include threads formed on a surface of the inner lumen 518.Similarly, the inner component 504 can be modified such that it does notinclude threads formed on the outer surface 706 thereof. As a result,the inner lumen 518 can slidably receive the outer surface 706 of theinner component. The inner component or inner lumen of the actuator caninclude a groove formed therein that can receive a set screw coupled tothe other component, similar to the mechanism described above withrespect to FIG. 9, to rotatably couple the actuator to the innercomponent. In other embodiments, a groove formed in the sidewall of oneof the components can be used in conjunction with one or more resilienttabs that extend into the groove when the inner component is slidablymated to the actuator. As a result, the inner component can be rotatablymated to the actuator and the actuator can subsequently be threaded intothe outer component as described above. The same protrusions 710 on theinner component can prevent it from rotating relative to the outercomponent as the actuator is rotated.

In still another embodiment, the actuator 506 and the outer component502 described above can be modified such that the outer surface of theactuator does not have threads 802 formed thereon and the inner surfaceof the outer component similarly does not have threads 512 formedthereon. As a result, the actuator can be slidably received within theinner lumen 603 of the outer component until a portion of the actuator,e.g., the enlarged diameter portion 524, abuts against a shelf or otherfeature of the outer component. In such an embodiment, the actuator canrotate relative to the outer component without translating, and theinner component can translate without rotating due to the threadedcoupling between the outer surface of the inner component and the innerlumen of the actuator in combination with the protrusions 710 and slots622.

Furthermore, the outer component can include a feature, such as a setscrew, pin, or other projection, that extends into a complementaryfeature, such as a groove formed around a circumference of the actuator,to prevent the actuator from being pushed proximally out of the outercomponent when, e.g., a distal force is applied to the compressionmember of a polyaxial screw by the inner component. In otherembodiments, one or more resilient tabs can be configured to extend intoa groove formed on either the outer component or actuator to provide thesame functionality. One of ordinary skill in the art will appreciatethat a number of other retention mechanisms can also be employed forthis purpose.

In addition to variations of the actuator, the outer component 502described above is one of a number of possible outer components that canbe configured to releasably couple to a receiving member of a polyaxialscrew. A number of additional mechanisms for releasably coupling with apolyaxial screw are described below and further explained in U.S. Pat.Nos. 7,179,261, 7,918,857, and 7,918,858, the contents of which arehereby incorporated by reference in their entirety.

FIGS. 10A-12 illustrate another embodiment of a screw extensioninstrument utilizing an alternative mechanism for engaging a receivingmember of a screw. With reference to FIGS. 10A and 10B, an outercomponent 900 is shown that includes an inner tube 1002 and an outertube 1004 disposed about at least a portion of the inner tube 1002. Inthe illustrated embodiment, the outer tube 1004 is coaxially disposedabout the inner tube 1002 such that the inner tube 1002 and the outertube 1004 share a common longitudinal axis 906. One skilled in the artwill appreciate, however, that the outer tube 1004 and inner tube 1002need not be coaxially aligned. The inner tube 1002 and the outer tube1004, in the exemplary embodiment, are generally cylindrical in shape,having an approximately circular cross-section. One skilled in the artwill appreciate, however, the inner tube 1002 and the outer tube 1004may have other cross-sectional shapes, including, for example,elliptical or rectilinear. In the exemplary embodiment, the inner tube1002 and outer tube 1004 have analogous cross-sections, however, oneskilled in the art will appreciate the inner tube 1002 and the outertube 1004 can have different cross-sectional shapes. The axial length ofthe inner tube 1002 and outer tube 1004 may vary depending on, forexample, the patient anatomy, the procedures employed, etc.

The inner tube or sleeve 1002 includes a proximal and a distal end, andhas an inner lumen extending between the proximal and distal ends. Theouter tube or sleeve 1004 similarly includes a proximal end and a distalend, and has an inner lumen extending between the proximal and distalends. The inner tube 1002 can be positionable within the inner lumen ofthe outer tube 1004. Furthermore, the inner tube 1002 can belongitudinally adjustable with respect to the outer tube 1004. Forexample, the inner tube 1002 may adjustable from a first, proximalposition, in which the distal end of the inner tube 1002 is positionedproximal to the distal end of the outer tube 1004 as illustrated in FIG.10B, and a second, distal position, in which the distal end of the innertube 1002 is positioned proximate to the distal end of the outer tube1004 (i.e., the inner tube 1002 is translated distally from the positionshown in FIG. 10B toward the distal end of the outer tube 1004). In theexemplary embodiment, the distal end of the inner tube 1002 preferablycontacts at least a portion of the polyaxial screw 100 when the innertube 1002 is in the second position.

In order to effect the relative movement of the inner tube 1002 and theouter tube 1004, the outer component 900 may include an adjustmentmechanism 902 that allows an operator to adjust the relativelongitudinal position of the inner tube 1002 and the outer tube 1004. Inthe illustrated embodiment, for example, the adjustment mechanism 902 isa hollow, tubular shaped cap having internal threads that engageexternal threads provided on the proximal end of the outer tube 1004.The threads allow the cap to be longitudinally adjusted relative to theouter tube 1004 independently of any adjustment of the inner componentrelative to the outer component, as described above. In the exemplaryembodiment, the inner tube 1002 can be connected to the cap and, thus,can move with cap as the cap is advanced or withdrawn relative to theouter tube 1004.

Similar to the screw extension instrument 500 discussed above, the innertube 1002 may have one or more sidewall openings or slots 904 formedtherein. In the illustrated exemplary embodiment, the inner tube 1002includes opposed slots 904 that extend longitudinally from the distalend of the inner tube 1002. Like the inner tube 1002, the outer tube1004 may have one or more sidewall openings or slots 905 formed therein.In the illustrated exemplary embodiment, the outer tube 1004 includesopposed slots 905 that extend longitudinally from the distal end of theouter tube 1004. The slots 904 and 905 can be used to facilitatepositioning of a spinal fixation element, such as a rod or a plate,relative to one or more bone anchors. To facilitate positioning of aspinal fixation element, the slots 904, 905 are preferably aligned withone another along at least a portion of the longitudinal axis of theouter component 900. The width and length of the slots 904, 905 may bevaried depending on the particular methods, instruments, and fixationelements being employed. In one exemplary embodiment, for example, thelength of the slots 904, 905 is selected to span at least from the skinincision to the distal end of the inner tube 1002 and the outer tube1004, respectively. In such embodiments, the slots 904, 905 may beaccessible from outside of the patient. In another exemplary embodiment,the length of the slots 904, 905 is selected to span from the distal endof the inner tube 1002 and the outer tube 1004, respectively, to a pointdistal to the skin incision. In such embodiments, the slots 904, 905 maybe accessible only from the inner lumens of the inner and outer tubes.

In embodiments in which multiple slots are employed, the slots 904, 905need not be similarly sized (width and/or length). For example, the oneor more of the slots 904 may be sized differently than the one or moreslots 905, the one or more of the slots 904 on the inner tube may besized differently than other slots 904, and/or one or more of the slots905 on the outer tube may be sized differently than other slots 905.Although the exemplary embodiment includes two opposing slots on theinner tube 1002 and the outer tube 1004, respectively, one skilled inthe art will appreciate that any number of slots may be provided, e.g.,no slots, one, two, three, etc. slots, may be provided depending on themethod, instruments, and/or fixation element employed.

The distal end of the outer tube 1004 includes a pair of opposedlongitudinally extending tabs 70A and 70B that may releasably engage abone anchor. In the exemplary embodiment, the tabs 70A and 70B aredefined by the sidewalls of the outer tube 1004 and are separated byslots 905. In certain exemplary embodiments, the tabs 70A and 70B may beflexible and resilient in the radial direction to facilitate connectionto a bone anchor. For example, the tabs 70A and 70B may be flexed apartin the radial direction from a first, relaxed position to facilitateadvancement of the tabs longitudinally over a portion of the boneanchor. Once positioned about a portion of the bone anchor, the tabs 70Aand 70B may provide a radially compressive force on the bone anchor asthe tabs 70A and 70B attempt to return to the first, relaxed position.In other exemplary embodiments, the tabs 70A and 70B need not beflexible and resilient.

Each tab 70A and 70B can include one or more radially inward facingprojections 72 that are sized and shaped to seat within an openingprovided in a portion of the receiving member of the polyaxial screw.The size, shape and number of projections can be varied depending on,for example, the opening(s) provided on the receiving member and thetype of connection desired. In the illustrated exemplary embodiment, forexample, each projection 72A, 72B is generally arcuate in shape and hasa cross section that is complementary to an arcuate groove 130 providedin the receiving member 108 of the exemplary polyaxial screw 100described above.

The distal end of the inner tube 1002 may include a contact surface 81that contacts at least a portion of the receiving member when the innertube 1002 is in the second position. In the illustrated exemplaryembodiment, for example, the distal end of the inner tube 1002 may havetwo opposing generally arcuate contact surfaces 81. The contact surfaces81, in the exemplary embodiment, are oriented approximatelyperpendicular to the longitudinal axis of the inner tube 1002. In theillustrated exemplary embodiment, the contact surfaces 81 are configuredto contact a generally arcuate contact surface provided on the proximalend of the receiving member 108 of the exemplary polyaxial screw 100.Preferably, the contact surface 81 is complementary in size, shape, andorientation to the contact surface on the bone anchor. One skilled inthe art will appreciate that the configuration of the contact surface81, e.g., number, size, shape, and orientation of the contact surface81, may be varied to, for example, suit the bone anchor being employed.

The distal end of the inner tube 1002 and/or the distal end of the outertube 1004 may be configured to inhibit rotation of the receiving memberrelative to the outer component 900. For example, the distal end of theinner tube may include one or more finger-like extensions 82 that extendapproximately axially from the distal end of the inner tuber 1002 andengage a bone anchor to inhibit rotation of the bone anchor relative tothe outer component 900. For example, one or more of the extensions 82may seat within a groove, recess, slot, or similar structure provided inthe bone anchor. Alternatively, one or more of the extensions 82 mayinclude a contact surface 84 for contacting an axially extending surface152 of the receiving member.

The outer component 900 illustrated in FIGS. 10A and 10B can be used inconjunction with the inner component 504 described above to provide ascrew extension instrument that can selectively and intraoperativelyconvert a polyaxial screw into a monoaxial screw while allowing for thepassage of a rod or other spinal fixation element through the receivingmember of the screw. In particular, an inner surface of the inner tubeor sleeve 1002 can include threads designed to engage with the outerthreaded surface 802 of the actuator 506, thereby providing longitudinaltranslation between the inner component and the outer component 900. Theprojection 710 of the inner component 504 can be configured to slidewithin the slot 904 to prevent the inner component from rotating withrespect to the inner tube or sleeve 1002 of the outer component 900.

FIG. 11 schematically illustrates the operation of a screw extensiondevice 1200 that includes the outer component 900 and inner component504. Shown in cross-section is the polyaxial screw 100 includingthreaded shank 106, head 104, receiving member 108, and compressionmember 204. Also shown is the outer component 900 securely andreleasably coupled to the receiving member 108. In particular, the outertube or sleeve 1004 of the outer component 900 is extended over theouter surface of the receiving member 108 and projections 72A, 72B areengaged with the groove 130 formed in the receiving member 108. Inaddition, the inner tube or sleeve 1002 of the outer component has beentranslated to the second position described above in which thecontacting surface 81 of the inner tube 1002 contacts an upper surfaceof the receiving member 108 to lock the connection between the outertube 1004 and the receiving member 108.

Also visible in the figure is the inner component 504 extending beyondthe distal end of the outer component 900 into the recess of thereceiving member 108. As described above, a distal surface of the innercomponent 504 is in contact with an upper surface of the compressionmember 204 and can apply a distal force to the compression member topress it into the head 104 and lock the orientation of the threadedshank 106 relative to the receiving member 108.

FIGS. 12A-12C illustrate the screw extension instrument 1200 of FIG. 11attached to a polyaxial screw 1202 implanted in a vertebra 1203. Thescrew extension instrument 1200 is shown extending through the muscleand tissue 1204 that lies above the vertebra, as would be the case in anMIS procedure. A second polyaxial screw attached to a screw extensiondevice is also visible implanted in an adjacent vertebra.

The close perspective view of FIG. 12B illustrates the connectionbetween the screw extension instrument 1200 and a receiving member 1206of the polyaxial screw 1202. In particular, an outer tube or sleeve 1208of an outer component of the instrument 1200 is disposed over a portionof an outer surface of the receiving member 1206, and an inner tube orsleeve 1210 of the outer component of the instrument has been advancedtoward a distal end of the outer tube 1208 to abut against an uppersurface of the receiving member 1206. The inner component of the screwextension instrument is not visible in this figure. FIG. 12C, incontrast, illustrates the screw extension instrument 1200 with the innercomponent 1212 advanced distally to apply a distal force to thecompression member 1214 of the polyaxial screw 1202 and thereby convertthe polyaxial screw into a monoaxial screw. In this configuration, asurgeon or other user can manipulate the proximal end of the screwextension instrument 1200 (see FIG. 12A) to adjust the position and/ororientation of the vertebra in which the polyaxial screw 1202 isimplanted. In addition, if desired, the surgeon or other user couldsubsequently retract the inner component 1212 proximally to convert themonoaxial screw back into a polyaxial screw. This process can berepeated as desired to switch between monoaxial and polyaxialconfigurations.

One skilled in the art will appreciate that the embodiments shown inFIGS. 5-12C are not the only possible mechanisms for releasably couplingan outer component of a screw extension instrument to a polyaxial screw.A number of other possible connection mechanisms are possible, includingthe threaded connection shown in FIGS. 13A-13B. In particular, an outercomponent 1300 can be provided having threads formed on an internalsurface of opposed arms 1301A, 1301B at its distal end. These threadscan engage with threads 1302 formed on an outer surface of a receivingmember 1304 of a polyaxial screw 1306.

In another embodiment shown in FIGS. 14A-14C, wires 1402 extending downthe opposed arms 1404A, 1404B of an outer component 1400 can be placedwithin grooves 1407 formed in a receiving member 1408 of a polyaxialscrew. The wires 1402 can be retracted proximally to securely andreleasably hold the receiving member 1408 in connection with the distalends of the opposed arms 1404A, 1404B.

In addition, alternative embodiments of an inner component are alsopossible. For example, the opposite-handed threads disposed on the innerand outer surfaces of the actuator need not be present. Instead, analternative embodiment can include a smooth-walled interface between theactuator 506 and inner component 504 with the use of a pin extendingfrom a sidewall of one component into a groove formed in the other. Inthis manner, the actuator would still be free to rotate and engage thethreads on the outer component, and the inner component would stilltranslate without rotating relative to the outer component.

As has been described above, the various embodiments of a screwextension instrument described herein can be formed in a variety ofsizes and shapes according to user desire, the type of procedureperformed, the type of polyaxial screw used, etc. For example, the axiallength of the outer component, inner component, and actuator can dependon patient anatomy, the procedures employed, and/or the area of thespine in which the instrument is employed. Furthermore, the instrumentsdescribed herein can be constructed from any suitable biocompatiblematerial, including, for example, a metal, such as stainless steel, or apolymer, and can be constructed using any conventional method ofmanufacturing medical devices.

The various embodiments of the devices described herein can be utilizedin a variety of surgical procedures—both in the spine and elsewhere inthe body. For example, the devices disclosed herein can be configuredfor use directly during an open surgical procedure, or they can beconfigured to be passed through one or more layers of tissue using oneor more incisions during a minimally invasive surgical (MIS) procedure.Regardless of the type of operation, the instruments described hereincan provide flexibility to surgeons by allowing for repeated andselective conversion of polyaxial screws to a monoaxial configurationwithout preventing the passage of a rod or other spinal fixation elementthrough the polyaxial screw. In addition, the screw extension instrumentprovides a convenient and effective tool for surgeons to manipulate toadjust the position and/or orientation of a vertebra after a polyaxialscrew has been converted to a monoaxial configuration.

In one embodiment, a method for correcting spinal deformities isprovided that can include coupling a screw extension instrument to areceiving member of a polyaxial screw that is coupled to a threadedshank that is polyaxially movable relative to the receiving member. Thiscan be accomplished using any of the various mechanisms describedherein—or others known in the art—for coupling an instrument to areceiving head of a polyaxial screw. The method can further includeadvancing an inner component of the screw extension instrument relativeto the receiving member of the polyaxial screw to cause the innercomponent to convert the polyaxial screw into a monoaxial screw. Thiscan be accomplished, for example, by advancing the inner component topush on a compression member disposed within a distal portion of thereceiving member of the polyaxial screw onto a head formed on thethreaded shank of the polyaxial screw to thereby prevent movement of thehead relative to the receiving member.

The method can include coupling the screw extension instrument to thereceiving member of the polyaxial screw either before or afterimplanting the threaded shank of the polyaxial screw in a vertebra of apatient. In addition, the method can include passing a spinal fixationelement, such as a spinal fixation rod, through the receiving member ofthe polyaxial screw after advancing the inner component of the screwextension instrument to convert the polyaxial screw into a monoaxialscrew. This can be done, for example, when a surgeon or other userwishes to provisionally correct the position and/or orientation of apatient's vertebra before passing a rod through the implanted polyaxialscrew or screws. To do so, the surgeon or other user can convert thepolyaxial screw to a monoaxial screw using a screw extension instrument,manipulate the screw extension instrument to provisionally correct thevertebra, and then pass a spinal fixation element through the polyaxialscrew.

Moreover, the method can also include retracting the inner component ofthe screw extension instrument relative to the receiving member toconvert the monoaxial screw into a polyaxial screw. Indeed, the processof advancing and retracting the inner component of the screw extensioninstrument can be repeated as many times as desired to continuallyconvert the polyaxial screw into a monoaxial configuration and viceversa. In some embodiments, for example, a surgeon or other user mayretract the inner component to return the screw to a polyaxialconfiguration after provisionally correcting the vertebra's position butbefore passing a spinal fixation element through the receiving member ofthe screw. By converting the screw back to a polyaxial configurationbefore passing a spinal fixation element, the surgeon or other user cantake advantage of the flexibility of polyaxial movement when passing thespinal fixation element.

Finally, the method can also include removing the inner component of thescrew extension instrument and inserting a closure mechanism into thereceiving member of the polyaxial screw. The closure mechanism can beused to permanently or temporarily fix the orientation of the receivingmember relative to the threaded shank, as well as the position and/ororientation of the polyaxial screw relative to the spinal fixationelement.

The devices disclosed herein can be designed to be disposed after asingle use, or they can be designed for multiple uses. In either case,however, the device can be reconditioned for reuse after at least oneuse. Reconditioning can include any combination of the steps ofdisassembly of the device, followed by cleaning or replacement ofparticular pieces, and subsequent reassembly. In particular, the devicecan be disassembled, and any number of the particular pieces or parts ofthe device can be selectively replaced or removed in any combination.Upon cleaning and/or replacement of particular parts, the device can bereassembled for subsequent use either at a reconditioning facility or bya surgical team immediately prior to a surgical procedure. Those skilledin the art will appreciate that reconditioning of a device can utilize avariety of techniques for disassembly, cleaning/replacement, andreassembly. Use of such techniques, and the resulting reconditioneddevice, are all within the scope of the present invention. For example,the screw extension instruments disclosed herein may be disassembledpartially or completely. In particular, the outer component, innercomponent, and actuator, as well as any smaller components thereof, canbe separated from one another.

Preferably, the devices described herein will be processed beforesurgery. First, a new or used instrument can be obtained and, ifnecessary, cleaned. The instrument can then be sterilized. In onesterilization technique, the instrument can be placed in a closed andsealed container, such as a plastic or TYVEK bag. The container and itscontents can then be placed in a field of radiation that can penetratethe container, such as gamma radiation, x-rays, or high-energyelectrons. The radiation can kill bacteria on the instrument and in thecontainer. The sterilized instrument can then be stored in the sterilecontainer. The sealed container can keep the instrument sterile until itis opened in the medical facility. In other embodiments, an instrumentcan be sterilized using any number of ways known to those skilled in theart including ethylene oxide, steam, autoclave, and a liquid bath (e.g.,cold soak).

All papers and publications cited herein are hereby incorporated byreference in their entirety. One skilled in the art will appreciatefurther features and advantages of the invention based on theabove-described embodiments. Accordingly, the invention is not to belimited by what has been particularly shown and described, except asindicated by the appended claims.

What is claimed is:
 1. A method for correcting spinal deformities,comprising: coupling a screw extension instrument to a receiving memberof a polyaxial screw, the receiving member being coupled to a threadedshank that is polyaxially movable relative to the receiving member;distally advancing relative to the receiving member of the polyaxialscrew opposed arms of an inner component of the screw extensioninstrument that are disposed radially inward from opposed arms of thereceiving member to exert a compressive force on a compression memberdisposed within the receiving member to convert the polyaxial screw intoa monoaxial screw; and retracting the inner component of the screwextension instrument relative to the receiving member to convert themonoaxial screw into a polyaxial screw after distally advancing theopposed arms of the inner component.
 2. The method of claim 1, whereindistally advancing the inner component of the screw extension instrumentcomprises pushing the compression member disposed within a distalportion of the receiving member of the polyaxial screw onto a headformed on the threaded shank of the polyaxial screw to thereby preventmovement of the head relative to the receiving member.
 3. The method ofclaim 1, further comprising implanting the threaded shank of thepolyaxial screw in a vertebra before coupling the screw extensioninstrument to the receiving member of the polyaxial screw.
 4. The methodof claim 1, further comprising implanting the threaded shank of thepolyaxial screw in a vertebra after coupling the screw extensioninstrument to the receiving member of the polyaxial screw.
 5. The methodof claim 1, further comprising passing a spinal fixation rod through thereceiving member of the polyaxial screw after advancing the innercomponent of the screw extension instrument to convert the polyaxialscrew into a monoaxial screw.
 6. A method for correcting spinaldeformities, comprising: coupling a screw extension instrument to areceiving member of a polyaxial screw, the receiving member beingcoupled to a threaded shank that is polyaxially movable relative to thereceiving member; converting the polyaxial screw to a monoaxialconfiguration in which the threaded shank is not movable relative to thereceiving member by distally advancing opposed arms of an innercomponent of the screw extension instrument that are disposed radiallyinward from opposed arms of the receiving member; and after convertingthe polyaxial screw to a monoaxial configuration, passing a spinalfixation element through the receiving member of the polyaxial screw. 7.The method of claim 6, further comprising implanting the threaded shankof the polyaxial screw in a vertebra of a patient.
 8. The method ofclaim 7, wherein coupling the screw extension instrument to thereceiving member of the polyaxial screw occurs after implanting thethreaded shank of the polyaxial screw.
 9. The method of claim 7, furthercomprising provisionally correcting any of a position and orientation ofthe vertebra after converting the polyaxial screw into a monoaxialconfiguration and before passing a spinal fixation element through thereceiving member of the polyaxial screw.
 10. The method of claim 9,further comprising, after provisionally correcting any of the positionand orientation of the vertebra and before passing the spinal fixationelement through the receiving member, converting the polyaxial screwfrom the monoaxial configuration back to a polyaxial configuration inwhich the threaded shank is polyaxially movable relative to thereceiving member using the screw extension instrument.
 11. The method ofclaim 6, further comprising, after passing the spinal fixation elementthrough the receiving member, inserting a closure mechanism into thereceiving member to fix the orientation of the receiving member relativeto the threaded shank.
 12. The method of claim 11, wherein the closuremechanism also fixes any of a position and orientation of the polyaxialscrew relative to the spinal fixation element.
 13. A method forcorrecting spinal deformities, comprising: coupling first and secondopposed arms of a screw extension instrument to an outer surface of areceiving member of a bone screw, wherein the first and second opposedarms are separated by first and second opposed slots that align with arecess defined by a U-shaped cross-section of the receiving member;rotating an actuator of the screw extension instrument in a firstdirection to effect distal translation of third and fourth opposed armsof the screw extension instrument that are disposed radially inward fromopposed arms of the receiving member to lock the receiving memberagainst movement relative to a threaded shank of the bone screw, whereinthe third and fourth opposed arms are aligned with the first and secondopposed arms and disposed radially inward therefrom; and distallytranslating fifth and sixth opposed arms of the screw extensioninstrument to contact a proximal-facing surface of the receiving memberafter coupling the first and second opposed arms to the outer surface ofthe receiving member; wherein the fifth and sixth opposed arms arealigned with the first and second opposed arms and are disposed radiallyinward from the first and second opposed arms and radially outward fromthe third and fourth opposed arms.
 14. The method of claim 13, furthercomprising rotating the actuator of the screw extension instrument in asecond direction to effect proximal translation of the third and fourthopposed arms of the screw extension instrument to permit movement of thereceiving member relative to the threaded shank of the bone screw. 15.The method of claim 13, wherein coupling the first and second opposedarms to the receiving member includes compressing a proximal portion ofthe screw extension instrument radially inward to cause a distal portionof the first and second opposed arms to move radially away from oneanother.
 16. The method of claim 13, further comprising implanting thethreaded shank of the bone screw in a vertebra of a patient.
 17. Themethod of claim 16, further comprising passing a spinal fixation elementinto the recess of the receiving member after rotating the actuator inthe first direction to lock the receiving member against movementrelative to the threaded shank of the bone screw.
 18. The method ofclaim 17, further comprising provisionally correcting any of a positionand orientation of the vertebra after rotating the actuator in the firstdirection to lock the receiving member against movement relative to thethreaded shank of the bone screw and before passing the spinal fixationelement into the recess of the receiving member.